[USN-4559-1] Samba update

---------- Forwarded message ---------

From: Marc Deslauriers <marc.deslauriers@canonical.com>

Date: Sep 30, 2020 10:29PM

Tom Tervoort discovered that the Netlogon protocol implemented by Samba

incorrectly handled the authentication scheme. A remote attacker could use

this issue to forge an authentication token and steal the credentials of

the domain admin.

While a previous security update fixed the issue by changing the "server

schannel" setting to default to "yes", instead of "auto", which forced a

secure netlogon channel, this update provides additional improvements.

For compatibility reasons with older devices, Samba now allows specifying

an insecure netlogon configuration per machine. See the following link for

examples: https://www.samba.org/samba/security/CVE-2020-1472.html

In addition, this update adds additional server checks for the protocol

attack in the client-specified challenge to provide some protection when

'server schannel = no/auto' and avoid the false-positive results when

running the proof-of-concept exploit.

References:

  https://usn.ubuntu.com/4559-1

  CVE-2020-1472